This invention relates to pneumatic controls, and more particularly to a novel instrument which functions as a pneumatic potentiometer. More specifically, this invention relates to an adjustable pressure supply which comprises a tubular plenum having compressed air flowing therethrough, and a pneumatic switch having an input adjustably connected to any one of a plurality of axially spaced ports in the plenum thereby to adjust the output pressure of the switch.
It has long been customary to employ pneumatic switches for controlling pneumatically operated devices. Typically such a switch can be adjusted linearly or rotatably in order intermittently to connect its output to any one of the plurality of different input pressures. One disadvantage of this type of switch is that each time it is shifted from one input pressure to the next, its output is isolated from the pressure supply so that pressure to the output is momentarily interrupted.
Another type of pneumatic control device embodies the use of a conventional pressure regulator, which can be interposed between an output and a supply of compressed air to throttle or otherwise adjust the pressure of the air as it passes through the regulator. The disadvantage of such regulators is that, in order to be accurate, output pressure is always proportional to a spring tension, and is independent of the input pressure.
It is an object of this invention, therefore, to provide a novel instrument capable of dividing a compressed air input of predetermined value into a plurality of different output pressures, each of which will constitute a predetermined different percentage of the input pressure.
Another object of this invention is to provide a pneumatic potentiometer or instrument which is connected to a tubular plenum having thereacross a predetermined pressure drop, and which is adjustable to divide the pressure drop into any one of a plurality of different output pressures each of which is proportional to a different, predetermined percentage of the pressure drop across the plenum.
A more specific object of this invention is to provide a novel instrument in which a supply of compressed air is applied to one end of a tube the opposite end of which exhausts to the atmosphere, and which at spaced points therealong is connected by a plurality of separate, tubular ducts to a control valve which is operable selectively to connect one of the ducts to the output of the valve, thereby to produce an output pressure which is equal to a predetermined percentage of the pressure drop in the supply tube.
Other objects of the invention will be apparent hereinafter from the specification and from the recital of the appended claims, specifically when read in conjuction with the accompanying drawings.